Internet telephony is becoming increasingly popular as a means to avoid the high cost of conventional wired-line telephone charges. It is also becoming popular due to additional features that may be provided over standard telephone usage, such as the availability of inexpensive multimedia sessions. Other features are also available due to the transfer of data in addition to voice messages, such as executing preferences in telephone software and call processing software. Further features may be provided through methods for initiating and processing call sessions.
Session Initiation Protocol (SIP) is a standard protocol for initiating an interactive user session involving multimedia elements such as video, games, voice, virtual reality and the like. As an example, SIP can establish and maintain Internet telephone calls. SIP provides application layer signaling that normally runs over User Datagram Protocol (UDP) or Transmission Control Protocol (TCP). The SIP standard is described further in the Internet Engineering Taskforce (IETF) RFC 3261, entitled “SIP: Session Initiation Protocol” and dated July 2002. As a request-response protocol, SIP accepts requests from clients and delivers responses from servers. Participants are identified by Universal Resource Identifiers (URIs). SIP establishes call parameters at either end of the communication session and handles call transfer and call termination.
Call processing languages may be used to tailor and adapt call control services to user preferences, and may be based on (or respond to) context information such as location, time, availability, or any other personal information. The Internet Engineering Task Force is currently standardizing a call processing language known as “CPL” that enables such call processing functionality (see IETF Internet Draft “draft-ietf-iptel-cpl-06.txt,” which expired July 2002). CPL allows a party who is registered with a SIP proxy to establish various options and parameters for call processing. In some circumstances, the party would be a calling party (or “inviting” party in SIP), and thus placing an outgoing call through the SIP proxy. In other circumstances, the party could be a called party (or “invited” party), and may be receiving an incoming call through the SIP proxy. In either case, the call processing options would be described in a CPL script that is uploaded to the registering SIP proxy. The CPL script enables (among other functions) examination of fields in an incoming INVITE (directed to the party) or outgoing INVITE (originating from the party). As described in the above-referenced IETF RFC 3261, an INVITE message is issued by a calling party in order to set up an Internet telephone or other multimedia communication. A SIP proxy (which may host the calling party or the called party) may then parse the INVITE message and, based on instructions contained in a CPL script (such as described above), execute various call processing options determined by information included in the INVITE message. By examining different parameters, keywords and other information in an INVITE message, a party may thus have numerous available alternatives with regard to incoming and outgoing calls or other communications.
is generally difficult, however, to dynamically adapt CPL-defined call-processing rules to changing situations. For example, there may be some circumstances in which a party (when functioning as the called party) may only wish to accept calls from certain persons. The party may further wish to direct all other calls to voicemail or to an assistant. In other circumstances, the party may be willing to accept calls from a larger group.
One possible solution requires the party to upload a new CPL script to his or her hosting SIP proxy whenever he or she wishes to change how calls will be processed. This would require knowledge of CPL scripts in the party's SIP client device, as well as the ability to store and/or edit CPL scripts. However, CPL scripts can be fairly complex, and are often constructed with web-based tools on a desktop PC (or other computer with similar functionality), and not on a mobile phone or other client device with more limited functionality. Adding the ability to store, edit and upload CPL scripts could significantly increase the complexity and cost of a mobile device.
Another possible solution is to perform call processing within an application program running upon a SIP client. In the case of an incoming call, this would require completing the call before any action regarding the call could be taken. Among other disadvantages, this may tie up the called party's resources with calls that he or she seeks to avoid or to reroute for handling by other persons.
Yet another possible solution involves use of an external trusted third party call processing entity, as discussed in related U.S. patent application Ser. No. 09/995,568 entitled “External Trusted Party Call Processing In SIP Environments.” As discussed therein, an “external-switch” element initiates a transfer of call processing from the executing SIP proxy to an URI specified as a parameter of the external-switch. The URI may correspond to an external trusted third party server, which proceeds with context-specific processing according to its programming. Through communication between the SIP client and the third party server, it would be possible to determine call processing based on the state of the called party (and indeed, realize solutions to even more complex problems). However, introduction of a third party server adds complexity to the SIP proxy due to the additional communication with the third party server.
Accordingly, a need remains for less complex solutions to the problem of determining call processing options based upon the state of a communication network user when acting as either a called or calling party.